The term "magnetizable material" as used in the following description refers to the component of the total magnetic recording medium (tape or disk) which is the carrier of magnetic signals, i.e., the iron oxide, barium ferrite, chromium oxide or fine metal particles in a pigment-binder system. The term "magnetizable layer" refers to the layer of a recording medium which contains the magnetizable material (e.g., pigment-binder layer). The terms "magnetic recording medium" and "recording medium" are defined as the article (e.g., tape or disk) which comprises the magnetizable layer on a backing or substrate.
Magnetic recording media are conventionally made by first making a pigment dispersion by milling the ingredients of the magnetizable layer, (e.g., polyurethane binder, gamma ferric oxide pigment, wetting agents, solvents, curing agent and lubricant) for sufficient time to obtain a uniform dispersion in an apparatus such as a ball mill or attrition mill. The dispersion is then applied in a coating process, such as gravure or knife-coating, to a flexible backing or substrate, (e.g., polyester film). After coating, the coated substrate undergoes orientation in a magnetic field to align the pigment particles (or, in the case of diskettes, randomization) after which the recording medium is dried in an oven.
Those skilled in the recording medium art are constantly searching for improved binder ingredients and formulations which yield improved electromagnetic output (signal-to-noise ratio SNR) or durability, and which also yield process improvements, such as shorter milling times or higher pigment concentration in the dispersion (resulting in less solvent use).
Electron beam curing of binder polymers for recording media magnetizable layers represents a major potential advance in the state of the art of manufacturing technology for the industry. Binder materials useful for electron beam cured magnetic coatings are designed to cure via a free-radical mechanism when exposed to ionizing radiation.
As used in this description, the term "cured" means polymerized or cross-linked into a set, stiff, or insoluble condition, and the term "curing" means cross-linking or further increasing polymer molecular weight to achieve a cured state.